Abstract

Transmission characteristics of microtapered long-period fiber gratings (MTLPGs) and their strain and temperature sensitivities with variations in the waist diameters are investigated theoretically and experimentally. Transmission characteristics of MTLPGs strongly depend on the waist diameter of the tapered optical fiber (TOF) because of the modification of the effective index difference between the core and the cladding modes. Based on the photoelastic effect, the resonant wavelengths of MTLPGs with variations in strain shift to shorter wavelengths. The strain sensitivity of the MTLPG with a waist diameter of 25 μm is improved by a factor of 20 compared with that of a 125 μm long-period fiber grating. The temperature sensitivities of MTLPGs are also enhanced by reducing the waist diameter of the TOF.

(a) Theoretical results for field distributions of the core and cladding modes in MTLPGs with different waist diameters of 125, 100, 75, 50, and 25 μm and (b) theoretical results for the normalized intensity profiles of core modes with variations in waist diameter.

(a) Experimental results for transmission spectra of the MTLPGs with various waist diameters. The measured mode field images of the cladding modes (HE1m) coupled from fundamental core mode (HE11) are shown in the insets. (b) Theoretical results for effective indices of the core and cladding modes with variations in waist diameter.

(a) Experimental (symbols) and theoretical (red line) results for resonant wavelength shifts of MTLPGs as functions of strain and (b) strain sensitivities of MTLPGs as a function of the waist diameter.